Excitability of motor cortex inhibitory circuits in Tourette syndrome before and after single dose nicotine

The functional anatomy of Gilles de la Tourette syndrome

Gilles de la Tourette syndrome (GTS) holds a prime position as a disorder transgressing the brittle boundaries of neurology and psychiatry with an entangling web of motor and behavioral problems. With tics as the disorder's hallmark and myriads of related signs such as echo-, pali- and coprophenomena, paralleled by a broad neuropsychiatric spectrum of comorbidities encompassing attention deficit hyperactivity disorder, obsessive-compulsive disorder and self-injurious behavior and depression, GTS pathophysiology remains enigmatic. In this review, in the light of GTS phenomenology, we will focus on current theories of tic-emergence related to aberrant activity in the basal ganglia and abnormal basal ganglia-cortex interplay through cortico-striato-thalamocortical loops from an anatomical, neurophysiological and functional-neuroimaging perspective. We will attempt a holistic view to the countless major and minor drawbacks of the GTS brain and comment on future directions of neuroscientific research to elucidate this common and complex neuropsychiatric syndrome, which merits scientific understanding and social acceptance.

Cholinergic dysfunction contributes to gait disturbance in early Parkinson's disease

Gait disturbance is an early feature in Parkinson's disease. Its pathophysiology is poorly understood; however, cholinergic dysfunction may be a non-dopaminergic contributor to gait. Short-latency afferent inhibition is a surrogate measure of cholinergic activity, allowing the contribution of cholinergic dysfunction to gait to be evaluated. We hypothesized that short-latency afferent inhibition would be an independent predictor of gait dysfunction in early Parkinson's disease. Twenty-two participants with Parkinson's disease and 22 age-matched control subjects took part in the study. Gait was measured objectively using an instrumented walkway (GAITRite), and subjects were asked to walk at their preferred speed for 2 min around a 25-m circuit. Spatiotemporal characteristics (speed, stride length, stride time and step width) and gait dynamics (variability described as the within subject standard deviation of: speed, stride time, stride length and step width) were determined. Short-latency afferent inhibition was measured by conditioning motor evoked potentials, elicited by transcranial magnetic stimulation of the motor cortex, with electrical stimuli delivered to the contralateral median nerve at intervals ranging from N20 (predetermined) to N20 + 4 ms. Short-latency afferent inhibition was determined as the percentage difference between test and conditioned response for all intervals and was described as the group mean. Participants were optimally medicated at the time of testing. Participants with Parkinson's disease had significantly reduced gait speed (P = 0.002), stride length (P = 0.008) and stride time standard deviation (P = 0.001). Short-latency afferent inhibition was also significantly reduced in participants with Parkinson's disease (P = 0.004). In participants with Parkinson's disease, but not control subjects, significant associations were found between gait speed, short-latency afferent inhibition, age and postural instability and gait disorder score (Movement Disorders Society Unified Parkinson's Disease Rating Scale) and attention, whereas global cognition and depression were marginally significant. No other gait variables were associated with short-latency afferent inhibition. A multiple hierarchical regression model explored the contribution of short-latency afferent inhibition to gait speed, controlling for age, posture and gait symptoms (Postural Instability and Gait Disorder score-Movement Disorders Society Unified Parkinson's Disease Rating Scale), attention and depression. Regression analysis in participants with Parkinson's disease showed that reduced short-latency afferent inhibition was an independent predictor of slower gait speed, explaining 37% of variability. The final model explained 72% of variability in gait speed with only short-latency afferent inhibition and attention emerging as independent determinants. The results suggest that cholinergic dysfunction may be an important and early contributor to gait dysfunction in Parkinson's disease. The findings also point to the contribution of non-motor mechanisms to gait dysfunction. Our study provides new insights into underlying mechanisms of non-dopaminergic gait dysfunction, and may help to direct future therapeutic approaches.

Nicotine up-regulated 4-1BBL expression by activating Mek-PI3K pathway augments the efficacy of bone marrow-derived dendritic cell vaccination

PURPOSE

To explore the role of 4-1BBL in nicotine-treated immature dendritic cells (imDCs) mediated anti-tumor effects.

METHODS

Bone marrow-derived imDCs were stimulated with nicotine and 4-1BBL expression was determinated by flow cytometry, Western blot and RT-PCR respectively. Then, the roles of 4-1BBL in nicotine-augmented DCs-dependent T cell proliferation, CTL priming and anti-tumor effects were investigated by BrdU cell proliferation assay, enzyme-linked immunospot assay and in vivo preventive effect on tumor development, respectively. Finally, using relative kinase inhibitors, the mechanism of 4-1BBL up-regulation by nicotine stimulation and the roles of Mek-PI3K signal pathways in nicotine-augmented DCs-dependent T cell proliferation were explored by Western blot and BrdU cell proliferation assay, respectively.

RESULTS

Firstly, nicotine could up-regulate 4-1BBL expression in both protein and mRNA levels. Secondly, the effects of nicotine-augmented DCs-dependent T-cell proliferation, CTL priming and anti-tumor effects could be significantly abolished by blocking CD80, CD86 and 4-1BBL activity, respectively. Thirdly, the combined blockages of CD80/CD86, CD80/4-1BBL, CD86/4-1BBL or CD80/CD86/4-1BBL signals could decrease 53.2 %, 29.6 %, 27.9 % and 54.5 % nicotine-enhanced T cell proliferation, respectively. Importantly, nicotine-induced 4-1BBL up-regulation could be decreased by the usage of Mek-PI3K pathway kinase inhibitors. The pre-treatment of Mek-p38-PI3K kinase inhibitors could obviously abolish nicotine-augmented DCs-dependent T cell proliferation.

CONCLUSIONS

CD80/CD86 and 4-1BBL are critical for nicotine augmented DCs-mediated anti-tumor effects. 4-1BBL and CD80/CD86 could be considered as potential candidates for preventive and therapeutic tumor vaccination.

The pathophysiology of echopraxia/echolalia: relevance to Gilles de la Tourette syndrome

Echopraxia and echolalia are subsets of imitative behavior. They are essential developmental elements in social learning. Their persistence or reemergence after a certain age, though, can be a sign of underlying brain dysfunction. Although echophenomena have been acknowledged as a typical sign in Gilles de la Tourette syndrome (GTS) since its first description, their clinical significance and neural correlates are largely unknown. Here, we review the course of their scientific historical development and focus on their clinical phenomenology and differential diagnosis with a particular view to GTS. The neural basis of echophenomena will also be addressed. © 2012 Movement Disorder Society.

Increased sensory feedback in Tourette syndrome

Tourette syndrome (TS) is a neuro-psychiatric disorder being characterized by motor and phonic tics typically preceded by sensory urges. Given the latter the role of the sensory system and sensorimotor interaction in TS has recently gained increased attention. 12 TS patients and 12 matched control subjects performed two tasks, requiring simple finger movements: a Go/NoGo task and a self paced movement task. Neurophysiological data was recorded using magnetoencephalography (MEG). Event related responses around movement onset, i.e. motor field (MF) occurring directly prior to the movement and movement evoked field (MEF) immediately after movement onset were analyzed using dipole modeling. MF peak amplitudes did not differ between groups in either task. In contrast, in both tasks MEF peak amplitudes were increased in TS patients. Moreover, larger MEF amplitudes during self paced movements were inversely correlated with motor tic frequency and severity. Enlarged MEF amplitudes as a marker of early sensory feedback of one's own movements probably represent enlarged sensory input from the periphery resulting from altered subcortical gating. We conclude that TS patients exhibit altered sensory-motor processing involved in voluntary movement control, which might also be successful in tic control.

Intentionality and "free-will" from a neurodevelopmental perspective

The nature of free-will as a subset of intentionality and probabilistic and deterministic function is explored with the indications being that human behavior is highly predictable which in turn, should compromise the notion of free-will. Data supports the notion that age relates to the ability to progressively effectively establish goals performed by fixed action patterns and that these FAPs produce outcomes that in turn modify choices (free-will) for which FAPs need to be employed. Early goals require behaviors that require greater automation in terms of FAPs that lead to goals being achieved or not; if not, then one can change behavior and that in turn is free-will. Goals change with age based on experience which is similar to the way in which movement functions. We hypothesize that human prefrontal cortex development was a natural expansion of the evolutionarily earlier developed areas of the frontal lobe and that goal-directed movements and behavior, including choice and free-will, provided for an expansion of those areas. The same regions of the human central nervous system that were already employed for better control, coordination, and timing of movements, expanded in parallel with the frontal cortex. The initial focus of the frontal lobes was the control of motor activity, but as the movements became more goal-directed, greater cognitive control over movement was necessitated leading to voluntary control of FAPs or free-will. The paper reviews the neurobiology, neurohistology, and electrophysiology of brain connectivities developmentally, along with the development of those brain functions linked to decision-making from a developmental viewpoint. The paper reviews the neurological development of the frontal lobes and inter-regional brain connectivities in the context of optimization of communication systems within the brain and nervous system and its relation to free-will.

Widespread abnormality of the γ-aminobutyric acid-ergic system in Tourette syndrome

Dysfunction of the γ-aminobutyric acid-ergic system in Tourette syndrome may conceivably underlie the symptoms of motor disinhibition presenting as tics and psychiatric manifestations, such as attention deficit hyperactivity disorder and obsessive-compulsive disorder. The purpose of this study was to identify a possible dysfunction of the γ-aminobutyric acid-ergic system in Tourette patients, especially involving the basal ganglia-thalamo-cortical circuits and the cerebellum. We studied 11 patients with Tourette syndrome and 11 healthy controls. Positron emission tomography procedure: after injection of 20 mCi of [(11)C]flumazenil, dynamic emission images of the brain were acquired. Structural magnetic resonance imaging scans were obtained to provide an anatomical framework for the positron emission tomography data analysis. Images of binding potential were created using the two-step version of the simplified reference tissue model. The binding potential images then were spatially normalized, smoothed and compared between groups using statistical parametric mapping. We found decreased binding of GABA(A) receptors in Tourette patients bilaterally in the ventral striatum, globus pallidus, thalamus, amygdala and right insula. In addition, the GABA(A) receptor binding was increased in the bilateral substantia nigra, left periaqueductal grey, right posterior cingulate cortex and bilateral cerebellum. These results are consistent with the longstanding hypothesis that circuits involving the basal ganglia and thalamus are disinhibited in Tourette syndrome patients. In addition, the abnormalities in GABA(A) receptor binding in the insula and cerebellum appear particularly noteworthy based upon recent evidence implicating these structures in the generation of tics.

Motor-cortical interaction in Gilles de la Tourette syndrome

Background

In Gilles de la Tourette syndrome (GTS) increased activation of the primary motor cortex (M1) before and during movement execution followed by increased inhibition after movement termination was reported. The present study aimed at investigating, whether this activation pattern is due to altered functional interaction between motor cortical areas.

Methodology/Principal Findings

10 GTS-patients and 10 control subjects performed a self-paced finger movement task while neuromagnetic brain activity was recorded using Magnetoencephalography (MEG). Cerebro-cerebral coherence as a measure of functional interaction was calculated. During movement preparation and execution coherence between contralateral M1 and supplementary motor area (SMA) was significantly increased at beta-frequency in GTS-patients. After movement termination no significant differences between groups were evident.

Conclusions/Significance

The present data suggest that increased M1 activation in GTS-patients might be due to increased functional interaction between SMA and M1 most likely reflecting a pathophysiological marker of GTS. The data extend previous findings of motor-cortical alterations in GTS by showing that local activation changes are associated with alterations of functional networks between premotor and primary motor areas. Interestingly enough, alterations were evident during preparation and execution of voluntary movements, which implies a general theme of increased motor-cortical interaction in GTS.

[Somatosensory phenomena and the role of sensorimotor circuits in Gilles de la Tourette syndrome]

Gilles de la Tourette syndrome (GTS) is characterized by multiple fluctuating motor and vocal tics. These tics are often preceded by premonitory phenomena including the urge to move, or by exaggerated bodily sensations that can lead to considerable disability and difficulties with attention and concentration. In the past the premonitory phenomena were interpreted as the driving force behind tics. However, there is not always a clear sequence of premonitory sensations followed by a tic. Also, the former typically develop around the age of 10 years, i.e. after the onset of the latter. Thus, the relationship between premonitory phenomena and tics is unclear. The present article reviews the current knowledge on this issue. Neurophysiological studies have shown some abnormalities of sensorimotor integration in GTS. In addition, structural imaging (MRT) has demonstrated a thinning of the sensorimotor cortex in children and adolescents with GTS. In contrast, an increase in fractional anisotropy as a marker of the directionality of white matter fibers underneath the pre- and postcentral gyrus has been demonstrated in adult GTS patients. These data underscore the role of developmental abnormalities and reorganisation in the somatosensory system in GTS warranting further studies. Multimodal studies including structural and functional imaging and electrophysiology in clinically well characterized GTS subgroups might foster a better understanding of somatosensory phenomena and the role of sensorimotor circuits in GTS.

European clinical guidelines for Tourette syndrome and other tic disorders. Part II: pharmacological treatment

To develop a European guideline on pharmacologic treatment of Tourette syndrome (TS) the available literature was thoroughly screened and extensively discussed by a working group of the European Society for the Study of Tourette syndrome (ESSTS). Although there are many more studies on pharmacotherapy of TS than on behavioral treatment options, only a limited number of studies meets rigorous quality criteria. Therefore, we have devised a two-stage approach. First, we present the highest level of evidence by reporting the findings of existing Cochrane reviews in this field. Subsequently, we provide the first comprehensive overview of all reports on pharmacological treatment options for TS through a MEDLINE, PubMed, and EMBASE search for all studies that document the effect of pharmacological treatment of TS and other tic disorders between 1970 and November 2010. We present a summary of the current consensus on pharmacological treatment options for TS in Europe to guide the clinician in daily practice. This summary is, however, rather a status quo of a clinically helpful but merely low evidence guideline, mainly driven by expert experience and opinion, since rigorous experimental studies are scarce.

Abnormal cortical and brain stem plasticity in Gilles de la Tourette syndrome

We investigated primary motor cortex and brain stem plasticity in patients with Gilles de la Tourette syndrome. The study group comprised 12 patients with Gilles de la Tourette syndrome and 24 healthy subjects. Patients were clinically evaluated using the Yale Global Tic Severity Scale. We tested cortical plasticity by conditioning left primary motor cortex with intermittent or continuous theta-burst stimulation in 2 separate sessions. Test stimulation consisted of 20 motor-evoked potentials recorded from right first interosseous muscle before and after theta-burst stimulation. We also tested brain stem plasticity by conditioning the right supraorbital nerve with facilitatory electric high-frequency stimulation delivered at the same time as the late response of the blink reflex or inhibitory high-frequency stimulation delivered before the late response on 2 separate sessions. Test stimulation consisted of 10 blink reflexes from the right orbicularis oculi muscle before and after high-frequency stimulation. After intermittent theta-burst stimulation, motor-evoked potential amplitudes in healthy subjects increased significantly but remained unchanged in patients. Similarly, after continuous theta-burst stimulation, motor-evoked potential amplitudes decreased significantly in healthy subjects but did not in patients. After facilitatory high-frequency stimulation, the blink reflex late response area in healthy subjects increased, whereas after inhibitory high-frequency stimulation, it decreased. Conversely, in patients, both interventions left the blink reflex late response area unchanged. The lack of the expected inhibitory and facilitatory changes in motor-evoked potential amplitudes and blink reflex late response area suggests that abnormal plasticity in the primary motor cortex and brain stem play a role in the pathophysiology of Gilles de la Tourette syndrome.

Momentary reward induce changes in excitability of primary motor cortex

OBJECTIVE

To investigate the human primary motor cortex (M1) excitability changes induced by momentary reward.

METHODS

To test the changes in excitatory and inhibitory functions of M1, motor-evoked potentials (MEPs), short-interval intracortical inhibition (SICI) and short-latency afferent inhibition (SAI) were tested in the abductor pollicis brevis (APB) muscle of non-dominant hand in 14 healthy volunteers by transcranial magnetic stimulation (TMS) during a behavioral task in which subjects were pseudorandomly received either reward target or non-target stimuli in response to a cue. To control sensorimotor and attention effects, a sensorimotor control task was done replacing the reward target with non-reward target.

RESULTS

The SICI was increased, and the SAI was decreased significantly during the presentation of the reward target stimuli. Those changes were not evident during non-reward target stimuli in the sensorimotor control task, indicating that this change is specific to momentary reward.

CONCLUSIONS

Momentary rewarding is associated with change in intracortical inhibitory circuits of M1.

SIGNIFICANCE

TMS may be a useful probe to study the reward system in health and in many diseases in which its dysfunction is suspected.

Altered pattern of motor cortical activation-inhibition during voluntary movements in Tourette syndrome

In patients with Gilles de la Tourette syndrome (GTS) alterations of motor cortex (M1) excitability at rest have been evidenced. In contrast, there has so far been little research into changes of motor cortical reactivity during the time course of voluntary movements in GTS patients. The present study investigates neuromagnetic event-related desynchronization (ERD) and event-related synchronization (ERS) of bilateral M1 in 11 GTS patients and 11 healthy control subjects. ERD represents motor cortical activation, whereas ERS most likely indicates its inhibition. Subjects performed a self-paced finger movement task while magnetoencephalography was used to record neuromagnetic activity. In GTS patients, ERD at beta frequency was significantly increased in the contralateral hemisphere before and during movements, whereas ERS following movement termination was increased in M1 ipsilateral. Ipsilateral ERS was inversely correlated with tic severity as determined by the Yale Global Tic Severity Rating Scale. The data of the present study support the hypothesis that during voluntary movements, motor cortical reactivity is pathologically altered in GTS patients. The observed pattern of increased activation (ERD) prior to and during movement execution followed by increased inhibition (ERS) after movement termination at beta frequency suggests abnormally increased motor cortical activation, possibly driving stronger inhibition. The stronger this inhibition is, the better symptoms appear to be controlled.

Linkage analysis of Tourette syndrome in a large Utah pedigree

Tourette syndrome (TS) is a neuropsychiatric disorder characterized by multiple motor and phonic tics. The heritability of TS has been well established, yet there is a lack of consensus in genome-wide linkage studies. The purpose of this study was to conduct a genome-wide linkage analysis on a unique, large, high-risk TS Utah pedigree. We examined a qualitative trait (TS1) where cases had a definitive diagnosis of TS as observed by a clinical interviewer (n = 66) and a quantitative phenotype based on the total Yale global motor and phonic tic severity scores (n = 102). Both parametric and non-parametric multipoint linkage analyses based on MCMC methods were performed using a 10 cM spaced micro-satellite autosomal marker set. Two regions of interest were identified under affecteds-only recessive models; a LOD score of 3.3 on chromosome 1p for Yale tic severity and a LOD score of 3.1 on chromosome 3p for the TS1 phenotype. Twenty-seven individuals shared linked segregating haplotypes for the 1p region. They had significantly higher Yale tic phonic scores than non-sharers (P = 0.01). There were 46 haplotype sharers on chromosome 3p with significantly higher percentage of females among these individuals compared to the non-sharers (P = 0.03). The significant linkage peaks on chromosomes 1p and 3p are in new areas of the genome for TS, and replication of these findings is necessary.

Electrophysiology in Gilles de la Tourette syndrome

Abnormalities in basal ganglia–thalamocortical circuits presumably play an important role in the pathophysiology underlying the chronic motor and vocal tics that define Gilles de la Tourette syndrome (GTS). Electrophysiological techniques, above all, the use of transcranial magnetic stimulation – a noninvasive and painless tool to examine the excitability of several different circuits in the human motor cortex – has advanced our understanding of the pathophysiology. Motor thresholds are similar in GTS and healthy subjects; in the resting state, recruitment of motor-evoked potentials above threshold is more gradual in patients with GTS compared with controls. By contrast, recruitment of motor-evoked potentials during preactivation is similar in both groups, as is the duration of the cortical silent period. This suggests that the distribution of excitability in the corticospinal system in patients at rest is different to that in healthy individuals. Importantly, correlation analysis has demonstrated that reduced levels of excitability at rest relate, in pure GTS patients, to video ratings of complex tics as well as hand and finger tics, with less excitability predicting fewer tics. The correlations disappear for measures made during voluntary activation. This suggests that this is an adaptive response to abnormal basal ganglia motor cortex inputs in an effort to reduce unwanted movements, a notion supported by electroencephalogram-coherence studies that demonstrated increased cortico–cortical coupling. Compared with the healthy control group, short intracortical inhibition thresholds are similar in patients with GTS. However, above threshold short intracortical inhibition recruitment and sensory afferent inhibition, a paradigm to examine sensory motor integration, is reduced in patients with GTS. This is consistent with the suggestion that reduced excitability of cortical inhibition is one factor that contributes to the difficulty that patients have in suppressing involuntary tics. In addition, the reduced sensory afferent inhibition indicates that impaired intracortical inhibition may not be limited to the motor cortex, but also involves circuits linking sensory input and motor output.

Transcranial magnetic stimulation in Gilles de la Tourette syndrome

The cause of Gilles de la Tourette syndrome (GTS), a chronic motor and vocal tic disorder of childhood onset, remains unknown. Abnormalities in basal ganglia-thalamo-cortical circuits presumably play an important role in the pathophysiology underlying the involuntary tics. The use of transcranial magnetic stimulation (TMS), a noninvasive and painless tool to examine the excitability of several different circuits in the human motor cortex has advanced our understanding of the pathophysiology. Motor thresholds are similar in GTS and healthy subjects; in the resting state, recruitment of motor evoked potentials (MEPs) above threshold is more gradual in patients than controls. In contrast, recruitment of MEPs during preactivation is similar in both groups, as is the duration of the cortical silent period. This suggests that the distribution of excitability in the corticospinal system in patients at rest is different to that in healthy individuals. Importantly, correlation analysis showed that reduced levels of excitability at rest relate, in pure GTS patients, to video ratings of complex tics, and hand and finger tics, with less excitability predicting fewer tics. The correlations disappear for measures made during voluntary activation. This suggests that this is an adaptive response to abnormal basal ganglia-motor cortex inputs in an effort to reduce unwanted movements, a notion supported by electroencephalography-coherence studies that show increased cortico-cortical coupling. Compared to the healthy control group, short intracortical inhibition (SICI) thresholds are similar. However, above-threshold SICI recruitment and sensory afferent inhibition (SAI), a paradigm to examine sensory motor integration, are reduced in patients. This is consistent with the suggestion that reduced excitability of cortical inhibition is one factor that contributes to the difficulty that patients have in suppressing involuntary tics. In addition the reduced SAI indicates that impaired intracortical inhibition may not be limited to the motor cortex but also involves circuits linking sensory input and motor output. GTS with attention deficit hyperactivity disorder comorbidity is associated with more extensive changes in the excitability of motor cortex circuits than pure GTS or GTS+obsessive-compulsive disorder. The extent to which various different neuronal circuits are affected may be relevant for the phenotype of Tourette spectrum disorders.

Influence of sympathetic autonomic arousal on tics: implications for a therapeutic behavioral intervention for Tourette syndrome

OBJECTIVES

The pharmacological treatment of Tourette syndrome (TS) has improved due to the application of new medications and combinations of medications, coupled to greater phenomenological and neurobiological understanding of the condition. Nevertheless, for many individuals with TS, potentially troublesome tics persist despite optimized drug treatment. Anecdotally, a relationship is frequently described between tic frequency and states of bodily arousal and/or focused attention. The galvanic skin response (GSR) is an accessible and sensitive index of sympathetic nervous activity, reflecting centrally induced changes in peripheral autonomic arousal. Sympathetic nervous arousal, measured using GSR, has been shown to have an inverse relationship with an electroencephalographic index of cortical excitability (slow cortical potential), and GSR arousal biofeedback shows promise as an adjunctive therapy in management of treatment-resistant epilepsy.

METHOD

We examined how changes in sympathetic arousal, induced using GSR biofeedback, impact on tic frequency in individuals with TS. Two different physiological states (sympathetic arousal and relaxation) were induced using GSR biofeedback in 15 individuals with a diagnosis of TS. During both biofeedback sessions, participants were videotaped to monitor the occurrence of tics.

RESULTS

We observed significantly lower tics during relaxation biofeedback compared to arousal biofeedback, with tic frequency positively correlating with sympathetic arousal during the arousal session.

CONCLUSION

These findings indicate that the conjunction of focused attention to task and reduced peripheral sympathetic tone inhibits tic expression and suggests a potential therapeutic role of biofeedback relaxation training for tic management in patients with TS.

Dopamine modulates cholinergic cortical excitability in Alzheimer's disease patients

In Alzheimer's disease (AD) patients dysfunction of cholinergic neurons is considered a typical hallmark, leading to a rationale for the pharmacological treatment in use based on drugs that enhance acetylcholine neurotransmission. However, besides altered acetylcholine transmission, other neurotransmitter systems are involved in cognitive dysfunction leading to dementia. Among others, dopamine seems to be particularly involved in the regulation of cognitive processes, also having functional relationship with acetylcholine. To test whether cholinergic dysfunction can be modified by dopamine, we used short latency afferent inhibition (SLAI) as a neurophysiological tool. First, we tested the function of the cholinergic system in AD patients and in healthy subjects. Then, we tested whether a single L-dopa challenge was able to interfere with this system in both groups. We observed that SLAI was reduced in AD patients, and preserved in normal subjects. L-dopa administration was able to restore SLAI modification only in AD, having no effect in healthy subjects. We conclude that dopamine can modify SLAI in AD, thus confirming the relationship between acetylcholine and dopamine systems. Moreover, it is suggested that together with cholinergic, dopaminergic system alteration is likely to occur in AD, also. These alterations might be responsible, at least in part, for the progressive cognitive decline observed in AD patients.

The management of tics

A tic is a stereotyped repetitive involuntary movement or sound, frequently preceded by premonitory sensations or urges. Most tic disorders are genetic or idiopathic in nature, possibly due to a developmental failure of inhibitory function within frontal-subcortical circuits modulating volitional movements. Currently available oral medications can reduce the severity of tics, but rarely eliminate them. Botulinum toxin injections can be effective if there are a few particularly disabling motor tics. Deep brain stimulation has been reported to be an effective treatment for the most severe cases, but remains unproven. A comprehensive evaluation accounting for secondary causes, psychosocial factors, and comorbid neuropsychiatric conditions is essential to successful treatment of tic disorders.

Structural changes in the somatosensory system correlate with tic severity in Gilles de la Tourette syndrome

Gilles de la Tourette syndrome (GTS) is a neuropsychiatric disorder characterized by multiple motor and vocal tics. Previous structural MRI studies have identified regional abnormalities in grey matter, especially in the basal ganglia. These findings are consistent with the assumption of alterations in cortico-striato-thalamo-cortical circuits and dopaminergic neurotransmission playing a major role in the pathophysiology of GTS. Additionally, recent imaging studies suggested an involvement of sensory-motor cortices in the pathophysiology of GTS. However, little is known about the role of white matter changes in GTS. In this study, we aimed to examine whether GTS is associated with abnormalities in white matter microstructure and whether these changes are correlated with tic severity. In a morphometric study based on diffusion tensor MRI of the whole brain, we compared brain tissue diffusion characteristics between 15 unmedicated adults with GTS without psychiatric co-morbidity and 15 healthy age- and sex-matched controls. We performed voxel-based morphometry (VBM) of regional fractional anisotropy (FA) values to identify regional differences in white matter microstructure between the groups. We also tested for a linear relationship between regional FA values and clinical scores of tic severity. Probabilistic fibre tracking was applied to characterize anatomical connectivity of those areas showing differences in regional FA. Compared with healthy controls, GTS patients showed bilateral FA increases in white matter underlying the post- and precentral gyrus, below the left supplementary motor area, and in the right ventro-postero-lateral part of the thalamus. The peak increase in FA was located below the left postcentral gyrus. Probabilistic tractography identified transcallosal and ipsilateral cerebello-thalamo-cortical pathways of the somatosensory system passing through this subcortical region. In patients, regional FA in this region showed an inverse linear relationship with tic severity. These findings demonstrate, for the first time, structural alterations in somatosensory pathways in GTS. Changes of water diffusion characteristics point towards reduced branching in somatosensory pathways in GTS patients. The negative correlation between higher regional FA values and fewer tics suggests that these alterations of white matter microstructure represent adaptive reorganization of somatosensory processing in GTS.

Consensus paper: use of transcranial magnetic stimulation to probe motor cortex plasticity in dystonia and levodopa-induced dyskinesia

Plasticity includes the ability of the nervous system to optimize neuronal activity at a cellular and system level according to the needs imposed by the environment. Neuroplasticity phenomena within sensorimotor cortex are crucial to enhance function to increase skillfulness. Such plasticity may be termed "adaptive" to indicate its ecologically beneficial role. In professional musicians, enhanced adaptive plasticity is associated with one of the highest level of motor skill a human being can achieve and the amount of these changes is even dependent on the age at which instrumental playing was started. In addition, adaptive neuroplastic changes occur when nervous system try to repair itself thus compensating dysfunctions. However, when these adaptive phenomena are pushed to an extreme, they can produce a maladaptive sensorimotor reorganization that interferes with motor performance rather than improving it. The model we discuss here is focal hand dystonia I which an intrinsic abnormality of neural plasticity, in some predisposed individuals, may lead to abnormal sensorimotor integration and to the appearance of a characteristic movement disorder. Deficient homeostatic control might be an important mechanism triggering this maladaptive reorganization, and future behavioral studies are needed to confirm this hypothesis. In the second part of this consensus paper, we will critically discuss as a second model, the hypothesis that levodopa-induced dyskinesia correlate with an aberrant form of plasticity in the human primary motor cortex, possibly because of abnormal oscillations within the basal ganglia loop. Disorders of cortical plasticity have not in the past been considered as possible causes of human clinical states. The recognition that this can occur, together with a speculative mechanism, generates an important and provocative hypothesis for future research at the clinical-scientific interface.

Cortical hypoexcitability in chronic smokers? A transcranial magnetic stimulation study

Studies in animal models and humans indicate that chronic nicotine intake influences neuronal excitability, resulting in functional and structural CNS changes. The aim of the present study was to explore human primary motor cortex (M1) excitability with transcranial magnetic stimulation (TMS) in chronic smokers. A total of 44 right-handed volunteers, aged 20-30 years, participated in the study. Chronic smokers were compared with age- and sex-matched healthy nonsmokers. We tested cortical excitability with single- and paired-pulse TMS to the left M1 and short-latency afferent inhibition (SAI) by combining median nerve stimulation and motor cortex TMS. Compared with nonsmoking controls, chronic smokers showed a significantly larger amount of SAI, which is thought to depend upon the activity of cholinergic inhibitory circuits produced by somatosensory inputs. Moreover, TMS-evoked inhibitory cortical silent periods were prolonged, whereas paired-pulse intracortical facilitation and motor-evoked potentials during moderate contraction were reduced. The results suggest that chronic nicotine intake may not only strengthen cholinergic inhibitory circuits, but could also be associated with enhanced inhibitory and reduced facilitatory mechanism of specific neuronal circuits in motor cortex. These changes may form a physiological basis for neurobiological and behavioral variations associated with chronic smoking.

Corticospinal system excitability at rest is associated with tic severity in tourette syndrome

BACKGROUND

Several measures of motor cortex excitability are abnormal in Gilles de la Tourette syndrome (GTS). However, it is not clear whether these represent abnormalities of specific pathways or reflect a more widespread reduction of motor cortex excitability. Their significance for the clinical phenotype is also unknown.

METHODS

We measured motor thresholds, input-output (I/O) curves, short interval intracortical inhibition (SICI), and cortical silent period (SP) with transcranial magnetic stimulation in 20 untreated GTS patients (12 uncomplicated, 4 with comorbid attention-deficit/hyperactivity disorder, 4 with comorbid obsessive-compulsive disorder) and 24 healthy subjects. Tics were rated with standard clinical scales and detailed video analysis.

RESULTS

Thresholds did not differ between groups. At rest, patients had shallower I/O curve slopes, despite their tics, and reduced SICI. Slopes were equal during voluntary muscle activation, as was the SP duration. Resting I/O slopes correlated, in uncomplicated GTS patients, most strongly to ratings of complex tics, hand and finger tics, and vocal tics, with shallower slopes predicting fewer tics. In complicated patients, good correlations were seen with neck/shoulder tics and vocal tics.

CONCLUSIONS

Corticospinal excitability in patients at rest is reduced. We suggest this is an adaptive response that may reduce release of unwanted movements.

Genetic variability in CYP2A6 and the pharmacokinetics of nicotine

Nicotine is the psychoactive substance responsible for tobacco dependence. It is also a therapeutic used to aid smoking cessation. Cytochrome P450 (CYP)2A6 is the human hepatic enzyme that mediates most of nicotine’s metabolic inactivation to cotinine. Genetic variation in the CYP2A6 gene can increase or decrease enzyme activity through altering the protein’s expression level or its structure and function. This article reviews CYP2A6 genetic variation and its impact on in vivo nicotine kinetics, including a description of the individual variants, different phenotyping approaches for assessing in vivo CYP2A6 activity and other sources of variation in nicotine metabolism such as gender. In addition, the effect of CYP2A6 polymorphisms on smoking behavior and tobacco-related lung cancer risk are briefly described. Furthering knowledge in this area will improve interpretation of studies examining smoking behavior, as well as those using nicotine as a therapeutic agent.

Functional involvement of cerebral cortex in adult sleepwalking

The pathophysiology of adult sleepwalking is still poorly understood. However, it is widely accepted that sleepwalking is a disorder of arousal. Arousal circuits widely project to the cortex, including motor cortex. We hypothesized that functional abnormality of these circuits could lead to changes in cortical excitability in sleepwalkers, even during wakefulness. We used transcranial magnetic stimulation (TMS) to examine the excitability of the human motor cortex during wakefulness in a group of adult sleepwalkers. When compared with the healthy control group, short interval intracortical inhibition (SICI), cortical silent period (CSP) duration, and short latency afferent inhibition (SAI) were reduced in adult sleepwalkers during wakefulness. Mean CSP duration was shorter in patients than in controls (80.9 +/- 41 ms vs. 139.4 +/- 37 ms; p = 0.0040). Mean SICI was significantly reduced in patients than in controls (73.5 +/- 38.4% vs. 36.7 +/- 13.1%; p = 0.0061). Mean SAI was also significantly reduced in patients than in controls (65.8 +/- 14.2% vs. 42.8 +/- 16.9%; p = 0.0053). This neurophysiological study suggests that there are alterations in sleepwalkers consistent with an impaired efficiency of inhibitory circuits during wakefulness. This inhibitory impairment could represent the neurophysiological correlate of brain "abnormalities" of sleepwalkers like "immaturity" of some neural circuits, synapses, or receptors.

Tic disorders: from pathophysiology to treatment

Tic disorders are stereotypic behaviours,more frequent than once believed, and therefore likely to be encountered by primary care physicians. Tics usually begin in childhood and are the clinical hallmark of Tourette Syndrome (TS), the most common cause of tics. TS is a relatively common neurobehavioural disorder with a spectrum of manifestations that wax and wane during its natural course. The pathophysiology of tics, at molecular and cellular level, is still unknown,whereas structural and functional neuroimaging studies have shown the involvement of the basal ganglia and related cortico-striato-thalamo-cortical circuits, and the dopaminergic neuronal system. Moreover, TS has a strong genetic background. The management of TS is often complicated by the presence of attention-deficit/hyperactivity disorder, obsessive-compulsive disorder, and other behaviour disorders. The correct diagnosis is a fundamental step for a proper management of these disorders, and a multimodal treatment is usually indicated. This approach includes educational and supportive interventions, as well as pharmacological treatments when tics are at their worst.

Effects of donepezil, nicotine and haloperidol on the central serotonergic system in mice: implications for Tourette's syndrome

We have previously reported that acute and chronic donepezil and nicotine administration significantly attenuate DOI-induced head twitch response (HTR) in mice. This behavior, primarily mediated by stimulation of 5-HT2A receptors, has been proposed to model tic symptoms seen in Tourette's syndrome (TS). Haloperidol, a drug widely used to treat symptoms of TS, has also been reported to reduce DOI-induced head shakes in rodents when administered acutely. These findings suggest an inhibitory interaction of these drugs with 5-HT2A receptors. To test this hypothesis, we evaluated the effects of chronic donepezil, nicotine and haloperidol on expression levels of 5-HT2A mRNA and 5-HT2A receptor density in select brain regions. Initially, we established a dose-response relationship for the acute and chronic haloperidol and DOI-induced HTR. Male ICR mice were treated twice daily with donepezil (0.1 mg/kg), nicotine (0.5 mg/kg), and once daily with haloperidol (0.4 mg/kg) for 14 days and were sacrificed 16-18 h after the last injection. These drug regimens were chosen because of their significant effects on DOI-induced HTR. Donepezil significantly increased 5-HT2A mRNA level, but not the receptor density in the striatum. In the midbrain, donepezil significantly decreased the receptor density without affecting the 5-HT2A mRNA level. In the frontal cortex, only haloperidol significantly reduced the 5-HT2A receptor density. The cortex was the only area where donepezil, nicotine and haloperidol significantly reduced the 5-HT2A receptor density. The results suggest that the anti-tic properties of donepezil, nicotine and haloperidol in this paradigm might be due to antagonism of cortical 5-HT2A receptors. Thus, further investigation of involvement of cortical 5-HT2A receptors in TS as well as evaluation of selective 5-HT2A receptor antagonists in this disorder is warranted.